Adaptive Test (AT) is a broad term used to describe methods that change test conditions, test flow, test content and test limits based on manufacturing test data and statistical data analysis. AT has been identified as an important test process and methodology change needed to achieve lower test costs, using the most recent release of the International Technology Roadmap for Semiconductors (ITRS http://www.itrs.net/). The term AT is not limited to semiconductors and can be applied to testing of other types of devices.
Attention is first drawn to FIG. 1 illustrating a generalized test system in accordance with the prior art.
FIG. 1 shows tests 351 (in the example of FIG. 1 T11 to T42) within a test flow 300 of tests accommodated in a test program 250. The tests may include group(s) of tests each containing a single test or multiple tests. The sequence in which the tests are executed, also known as an execution sequence of tests 400, may be determined, in real-time, by the operating system (OS) of the test system 200 at least in part based on the test flow 300. A sequence of operations in accordance with the prior art is shown in FIG. 7. During real-time AT based on manufacturing test data and/or statistical data analysis certain group(s) of tests (hereinafter group of tests that are candidates for removal) may be removed from the execution sequence, and are sometimes also referred to as bypassed, skipped or disabled groups. Such group(s) of tests that are removed from the execution sequence are not executed by the test system.
Dynamically modifying the execution sequence of tests on a test system (100) based on manufacturing test data and statistical data analysis can be used to reduce test time—Adaptive Test Time Reduction (ATTR), to improve yield or to prevent damage to devices or their reliability. Modification of test process or content can be performed in real-time without changing test programs. One of the main challenges of real-time dynamical modification of test process or content, is uncertainty whether subsequent tests will remain stable after a group of tests is removed from the execution sequence.
In addition to a logical dependence between tests, a given group of tests (i.e. one or more tests) may inter alia serve as a time buffer for settling of residual noise left from preceding test or tests, thus enabling tests following after such a group to be executed properly. The residual noise results from a well-known phenomenon that devices cannot respond instantaneously and will exhibit transient responses when they are subjected to inputs or disturbances. During testing, both devices under test (DUT) (referred to more generally as tested objects) and devices within components of a testing system, can be sources of said residual noise. Depending on type of the DUT and the testing system, the residual noise can be electrical, mechanical, thermal, electromagnetic, etc. The noise can be analog or digital. Settling time may be referred to as the time elapsed from the application of an ideal instantaneous step input to the time at which the device output has entered and remained within a specified error band. It may be difficult to identify or characterize the dependency on the given group of tests to serve as a buffer for settling at the time of real-time AT and therefore there may be uncertainty about how subsequent remaining tests will perform if a group of tests is removed from the execution sequence.
Because of this uncertainty, real-time AT is often replaced by test program re-structuring followed by a lengthy test program qualification.
References considered to be relevant as background to the presently disclosed subject matter are listed below:
http://www.semi.org/en/sites/semi.org/files/docs/ITRS_AdaptiveTest_WhitePaper2013.pdf
https://en.wikipedia.org/wiki/Settling_time.
https://www.lens.org/lens/search?q=settling+time+%26%26+test+time+reduction&1=en
https://www.lens.org/lens/patent/US_7646204_B2 “Method And System For Testing A Settling Time For A Device-under-test”
https://www.lens.org/lens/patent/US_5726996_A “Process For Dynamic Composition And Test Cycles Reduction”
https://www.lens.org/lens/search?q=settling+time+%26%26+test+reordering&1=en
https://www.lens.org/lens/patent/US_2013_0006567_A1 “Method And Apparatus For Scheduling A Use Of Test Resources Of A Test Arrangement For The Execution Of Test Groups”
Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.
There is thus a need in the art for a new technique for dynamically modifying an execution sequence of tests in real time.